What to do about the plastic waste in face masks?

People with masks are now a common sight now around the world.
Some of the masks are sewn at home, others professionally made. And then there are the disposable masks – the ones also used in hospitals.
They pose a huge risk to the environment, because they contain plastic. And often enough, they end up polluting rivers and oceans.
We can’t stop using masks. But we should not have to choose between saving lives or the environment. What should be done?